# List of Abstracts

## Abstracts of Worldwide Participants

**Shadow of rotating non-Kerr black hole**

#### Abdujabbarov Ahmadjon

We present analytical solutions of Maxwell’s equations around a rotating non-Kerr black hole immersed in an external uniform magnetic field. The influence of a magnetic field on the effective potential of the radial motion of a charged test particle around a rotating non-Kerr black hole immersed in an external magnetic field are investigated. The shadow of a rotating non-Kerr black hole has been studied, and it was shown that in addition to the specific angular momentum a, the deformation parameter of non-Kerr spacetime essentially deforms the shape of the black hole shadow.

**Vacuum Electromagnetic Fields and Plasma Magnetosphere of Magnetized Neutron Stars and Magnetars in General Relativity**

#### Ahmedov Bobomurat

The electromagnetic fields and magnetosphere of a slowly rotating magnetized neutron star subject to toroidal oscillations in the relativistic regime are studied. We analyse the Goldreich–Julian charge density and derive the modification induced by stellar toroidal oscillations on the accelerating electric field and on the charge density in the polar cap. We also find that, after decomposing the oscillation velocity in terms of spherical harmonics, the first few modes with m = 0, 1 are responsible for energy losses that are almost linearly dependent on the amplitude of the oscillation and that, for the mode (l,m) = (2, 1), can be a factor about 8 larger than the rotational energy losses, even for a velocity oscillation amplitude at the star surface small. The results obtained clarify the extent to which stellar oscillations are reflected in the time variation of the physical properties at the surface of the rotating neutron star, mainly by showing the existence of a relation between spindown and the oscillation amplitude. We propose a qualitative model for the explanation of the phenomenology of intermittent pulsars. The idea is that stellar oscillations, periodically excited by star glitches, can create relativistic winds of charged particles

because of the additional electric field. When the stellar oscillations damp, the pulsar shifts below the death line in the P–B diagram, thus entering the OFF invisible state of intermittent pulsars. The conditions for radio emission in rotating and oscillating magnetars by focusing on the main physical processes determining the position of their death lines, i.e. of those lines that separate the regions where the neutron star may be radio loud or radio quiet. We find that larger compactness parameters of the star as well as larger inclination angles between the rotation axis and the magnetic moment produce death lines well above the majority of known magnetars. This is consistent with the observational evidence of no regular radio emission from the magnetars in the frequency range typical for the ordinary pulsars. On the contrary, when

oscillations of the magnetar are taken into account, the death lines shift downward and the conditions necessary for the generation of radio emission in the magnetosphere are met. Present observations showing a close connection between the burst activity of magnetars and the generation of the radio emission in the magnetar magnetosphere are naturally accounted within our interpretation.

We revisit particle acceleration in the polar cap region of a neutron star by taking into account both general relativistic effects and the presence of toroidal oscillations at the star surface. In particular, we address the question of whether toroidal oscillations at the stellar surface can affect the acceleration properties in the polar cap. We solve numerically the relativistic elec-trodynamics equations in the stationary regime, focusing on the computation of the Lorentz factor of a space-charge-limited electron ow accelerated in the polar cap region of a rotating and oscillating pulsar. To this extent, we adopt the correct expression of the general relativistic Goldreich-Julian charge density in the presence of toroidal oscillations. Depending on the ratio of the actual charge density of the pulsar magnetosphere to the Goldreich-Julian charge density, we distinguish two different regimes of the Lorentz factor of the particle flow, namely an oscillatory regime produced for sub-GJ current density configurations, which does not produce an efficient acceleration, and a true accelerating regime for super-GJ current density configurations. We find that star oscillations may be responsible for a signicant asymmetry in the pulse profile that depends on the orientation of the oscillations with respect to the pulsar magnetic field. In particular, significant enhancements of the Lorentz factor are produced by stellar oscillations in the super-GJ current density regime.

We attempt to explain the subpulse drift phenomena adopting the space-charge limited low (SCLF) model and comparing the plasma drift velocity in the inner region of pulsar magne-tospheres with the observed velocity of drifting subpulses. We apply the approach described in a recent paper of van Leeuwen Timokhin (2012), where it was shown that the standard estimation of the subpulse drift velocity through the total value of the scalar potential drop in the inner gap gives inaccurate results, while the exact expression relating the drift velocity to the gradient of the scalar potential should be used instead. After considering a selected sample of sources taken from the catalog of Weltevrede, Edwards Stappers (2006) with coherently drifting subpulses and reasonably known observing geometry, we show that their subpulse drift velocities would correspond to the drift of the plasma located very close or above the pair for-mation front. Moreover, a detailed analysis of PSR B0826-34 and PSR B0818-41 reveals that

the variation of the subpulse separation with the pulse longitude can be successfully explained by the dependence of the plasma drift velocity on the angular coordinates.

**TBA**

#### Čadež Andrej

TBA

Gravity: On matters of principle and concept

#### Dadhich Naresh

TBA

**Resolving the unresolvable - polarimetry of active galactic nuclei at multiple wave bands**

#### Goosmann René

Polarization encodes geometry information of unresolvable sources. So far, the wavelength range at which polarized light can put constraints on the accretion and ejection flow around supermassive black holes extends from the radio to the ultraviolet band. In the future, we hope to also have access to X-ray polarization measurements. They will allow us to further zoom in on the innermost parts of AGN and to explore General Relativity effects at work very close to the supermassive black hole. Based on theoretical modeling, I lay out some prospects for future polarimetry techniques in the AGN field and I discuss some of the open questions we hope to solve.

**What X-ray astronomy can tell us about accreting black holes**

#### Goosmann René

Accreting black holes can be classified as active galactic nuclei, Galactic X-ray binaries or ultraluminous X-ray sources. All three classes have in common to produce strong X-ray emission coming from the innermost regions of the accretion flow. Not all matter that is pulled in by the black hole actually becomes accreted - a large portion of it is re-ejected in winds or even ballistic jets that can also be probed by X-ray observations. In this pedagogical presentation, I give an overview of the X-ray phenomenology of accreting black holes and I show how the last generation of X-ray observatories has shaped our understanding of these objects.

**Electromagnetic structure two-fluid plasma flow onto a black hole**

#### Kojima Yasufumi

In this presentation, we consider plasma flow, which consists of positively and negatively charged particles. By numerically solving the stationary electromagnetic fields, we discuss how the electric potential in Kerr space-time is induced.

**Primordial black holes as dark matter - revisited**

#### Miller John

A recent controversial paper by Pani & Loeb claims to virtually rule out the possibility that primordial black holes could be the dominant component of the dark matter. Their paper raises several interesting issues concerning tidal friction, neutron-star perturbations and accretion theory. This talk will present an updated review of the subject, focused particularly on those issues.

**Some observational properties of neutron stars**

#### Miller John

TBA

**Confronting models for the HF QPOs**

#### Stefanov Ivan

HF QPOs observed in the power-density spectra of several low-mass X-ray binaries containing a black hole or a neutron star have attracted significant research efforts due to their potential to provide information for the properties of the massive compact objects, for their accretion discs and for strong field gravity in general. Currently, none of the large number of models for the HF QPOs that can be found in the literature is commonly accepted. Here we discuss some possibilities for the testing of the models. We do not compare the predictions of the different models for the HF QPOs to the predictions of other methods but rather, starting from simple assumptions, look for inner inconsistencies.

**Modeling of coalescing vacuum gravitational-wave sources**

#### Taracchini Andrea

Coalescing compact binaries are promising sources of gravitational waves for the next generation of

ground-based interferometers (advanced LIGO and Virgo). An accurate knowledge of plausible gravitational-wave signals, as predicted by general relativity, is crucial for direct detection, as well as for the accurate extraction of physical information about the sources. I will review the main approaches to modeling these systems with a particular focus on stellar-mass black-hole binaries undergoing inspiral, merger and ringdown.

**Inverse kinetic theory for quantum hydrodynamic equations**

#### Tessarotto Massimo

The connection between quantum mechanics and classical statistical mechanics has motivated in the past the representation of the Schroedinger quantum-wave equation in terms of "projections" onto the quantum configuration space of suitable phase-space asymptotic kinetic models. This feature has suggested the search of a possible exact super-dimensional classical dynamical system (CDS), denoted as Schroedinger CDS, which uniquely determine the time-evolution of the underlying quantum state. In this paper the approach earlier developed and based on the adoption of an inverse kinetic theory is reviewed.

**The Principles of Kinetic Theory for Granular Matter**

#### Tessarotto Massimo

In this investigation the problem is posed of determining an exact, i.e., non-asymptotic, statistical description holding for non-relativistic classical granular matter, to be considered as a granular uid or gas. The latter is represented for this purpose in terms of a classical dynamical system (CDS) formed by a
nite number of smooth hard spheres which undergo instantaneous elastic collisions only, i.e., without the occurrence of any other possible interaction. Despite its simplicity, the considered physical model is of fundamental relevance for its basic implications.In fact it applies to a disparate variety of physical con-texts, ranging from astrophysics, environmental and biological uid dynamics and to industrial granular matter processing. Based on the emerging new ax-

iomatic approach to Classical Statistical Mechanics recently achieved, an exact particular realization is sought for the microscopic statistical description associated with the instantaneous elastic collisions. It is shown that the corresponding 1-body PDF

for such a CDS obeys a well-de
ned statistical equation, referred to as Master kinetic equation, which realizes an exact kinetic equation for granular matter, which holds both for dense and rare
ed systems. Its comparison with former approximate kinetic equations for dense granular matter is discusssed, while its asymptotic approximation in validity of the Boltzmann-Grad limit is shown to recover the customary Boltzmann equation holding for continuum rare
ed gases.

**Outburst properties evolution of ESO 243-49 HLX-1**

#### Zhen Yan

Hyperluminous X-ray source ESO 243−49 HLX-1 shows quasi-periodic outbursts in the past few years. We have performed a study of the outburst properties of HLX-1 with Swift/XRT monitoring observations. We found that the waiting time was increasing with the outburst sequence. We also found that the outburst duration, total radiated energy, and e-folding decay timescale were decreasing with the outburst sequence, which was also noticed by previous study. So during each cycle, HLX-1 spent less and less time during the outburst phase and more and more time during the quiescence phase in the sequence of last five outbursts. We compared the outburst properties of HLX-1 with bright Galactic low-mass X-ray binary transients (LMXBTs), and found that HLX-1 does not follow most correlations we found in bright Galactic LMXBTs if its distance is 95 Mpc, which indicate that they do not share the same outburst mechanism.

## Abstracts of Participants from Prague Astronomical Institute

**Oscillations of magnetized relativistic tori**

#### Hamerský Jaroslav

I will summarize our results of triggered large-scale oscillations of relativistic accretion tori in 2D. These oscillations cause that material

of the torus is wrenched above the equatorial plane and finally accelerated by centrifugal and magnetic pressure forces. I discuss the role of the strong magnetic field on the process of acceleration.

**An analogy of black-hole quasinormal modes in acoustic oscillations of relativistic accretion disks**

#### Horák Jiří

TBA

**Elektrodynamika černých děr**

#### Karas Vladimír

Elektrodynamika černých děr studuje různé aspekty interakce silných gravitačních polí černých děr s elektromagnetickými poli. Astronomové se domnívají, že tato teorie je relevantní pro existující kosmické objekty v jádrech galaxií. Jedním z projevů jsou mohutné kolimované výtrysky plazmatu dosahující daleko za hranice mateřské galaxie. V přednášce budou představena základní fakta o zmíněné interakci mezi černými děrami a kosmickými elektromagmetickými poli z pohledu astronomie.

**How X-ray polarimetry can unveil the history of the Galactic center**

#### Marin Frédéric

Despite numerous attempts with spectroscopic and timing analyzes, the origin of irradiation and fluorescence of the 6.4 keV bright giant molecular clouds surrounding Sgr A* , the central supermassive black hole of our Galaxy, remains enigmatic. The detection of these peculiar X-ray features is known for nearly twenty years now and is commonly associated with a past outburst of Sgr A* whose radiation is reprocessing onto the so-called “reflection nebulae”. In order to precisely test the alleged theory of a past active period of Sgr A∗, it is required to open a new observational window: X-ray polarimetry. In this presentation, we summarize the results from past and current polarimetric simulations in order to show how a future X-ray polarimeter equipped with imaging detectors could improve our understanding of high-energy astrophysics.

**Strong gravity with Athena**

#### Svoboda Jiří

I will briefly summarise how the X-ray spectroscopy is used for studying strong gravity around super-massive black holes in active galactic nuclei. I will discuss the expected scientific outcome with the next large X-ray mission planned by ESA, Athena.

## Abstracts of Participants from Silesian University in Opava

**Family of Schwarzschild-like solutions and firewall**

#### Blaschke Martin

TBA

**Poklady fyziky: Entropie černých děr**

Blaschke Martin

TBA

**Modified BBGKY hierarchy for the hard-sphere system**

#### Cremaschini Claudio

A statistical approach is presented for the study of classical N-body systems formed by hard smooth spheres. Based on an axiomatic approach to Classical Statistical Mechanics recently developed, modified collision boundary conditions for the N-body probability density are introduced, which apply also to dense or locally-dense hard-sphere systems. As a result, a modified form is determined for the BBGKY hierarchy, which is characterized by a new representation for the s-body collision operator. The same hierarchy is found to admit both stochastic and deterministic particular solutions. As an application, in the Boltzmann-Grad limit the hierarchy is shown to recover the ordinary Boltzmann equation holding in the case of rarefied gases.

**Oscillations of a charged particle moving around a black hole immersed in magnetic field**

#### Kološ Martin

We discuss the motion of charged test particles in a spacetime of a static non-rotating Schwarzshild black hole immersed in uniform magnetic field. Initially we suppose the neutral particle moving along the circular orbit, but when the particle we will charged, the quasi-periodic oscillations will appear. We compare charged particle oscillatory frequencies with the frequencies of high-frequency quasi-periodic oscillations observed in the microquasars GRS 1915+105, XTE 1550-564, GRO 1655-40.

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**Pozorování (nejen) proměnných hvězd na dalekohledu D65 v Ondřejově**

#### Kučáková Hana

TBA

**On the ideal spherically symmetric Einstein-charged perfect fluid system**

#### Pugliese Daniela

We examine the stability of an ideal, spherically symmetric Einstein-charged perfect fluid configurations by means of a 1+1+2-tetrad formalism. We show how this formalism can be used to cast, in a symmetric hyperbolic form, independent of any geometric gauge considerations, the equations describing the evolution of the system. This hyperbolic reduction is used, in turn, to discuss the stability of solutions to the linearised equations. By restricting the analysis to isotropic fluids configurations we made use of a constant electrical conductivity coefficient for the fluid (plasma), and the nonlinear stability for the case of an infinitely conducting plasma is also considered. As a result of this analysis we provide a classification of various stable kinematical configurations, we found in particular that in many cases the stability conditions can be strongly determined by the constitutive equations by means of the square of the velocity of sound and the electric conductivity.

**Imprints of Sphericaly Symmetric Regular Spacetimes in Keplerian discs images**

#### Schee Jan

We present our recent study on particular optical phenomena taking place in the vicinity in horizon-less compact object generating spherically symmetric, static, regular spacetime. The effect in question is the presence of additional image (ghost image) in the primary image of Keplerian disc. We will discuss the relationship between the ghost image specific parameters and charge parameter *g* characterizing the self-gravitating charged sources governed by Einstein’s gravity and non-linear electrodynamics.

**Co-rotation radius around rotating neutron stars**

#### Urbanec Martin

In this presentation I will present behavior of the position of the co-rotation radius, where the orbital frequency of the particle is corresponding to the rotation frequency of the central neutron star. The behavior of this position is studied within the Hartle-Thorne approximation.

## Abstracts of Student talks from Silesian University in Opava

**Mnoho tváří Slunce**

Exnerová Martina

Před čtyřista lety jsme jako lidstvo poprvé spatřili Slunce dalekohledem a zjistili, že není dokonalé. Začali jsme zaznamenávat sluneční skvrny a s nástupem lepší a lepší techniky i další bohaté projevy jeho aktivity. Sluneční erupce, protuberance, spikule, flokule... a další úkazy se před vědci se speciálními dalekohledy začali zjevovat a otevírat nám tak nové obzory k fungování Slunce a jeho magnetického pole. S postupem času se kdysi drahá technika stala finančně dostupnější a tak se i nadšenci pro Slunce mohou dostat ke speciálním dalekohledům stejně snadno jako milovníci noční oblohy. Co všechno nám sluneční filtry přináší, jaká jsou jejich úskalí a co s nimi můžeme pozorovat, na to se pokusí odpovědět právě tato přednáška.

**Extreme gravitational lensing**

#### Klimeš Marcel

Overview of contemporary progress and our results in field of modeling extreme gravitational lensing near black holes using our customized computational software. Comparison of different situations, pointing out new approaches, improvements and plans for the future.

**Comparison of a uniform magnetic field with a dipole-type around the planet Saturn**

#### Sysel Vojtěch

We describe a model of rotating dipole-type magnetic field around the planet Saturn and than we compare that with a model of rotating uniform magnetic field. The focus of comparison is to find common type of extreme in a potencial field od models.

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**The motion of irregular and dwarf galaxies in the framework of the MOND theory**

#### Šimeček Patrik

TBA